1. Field of the Invention
The present invention relates to a control circuit for a construction machine for switching a plurality of actuators.
2. Description of the Related Art
Conventionally, a hydraulicexcavator equipped with a boom swing apparatus is known, for excavating a small place at the corner by swinging a boom left and right around a vertical axis. As an operating means for operating a boom swing cylinder, there is an operating means in which a foot pedal is used. Such an equipment with the foot pedal limits space in foot side. Also, equipment with a nibbler or a breaker as an option increases the number of pedals and makes operations thereof complex.
For this reason, an operation lever can be used, which performs together operation of the boom swing cylinder and operation of an actuator, for example a revolving motor that is not operated in combination of boom swing.
In this case, when after switching from revolving to boom swing, if the switching operation is not recognized, there is a problem that mis-operation can occur that the revolving is derived from the operation carried out for a boom swing purpose.
An object of the present invention is to provide a control circuit for a construction machine capable of certainly preventing wrong operation in a case that a plurality of actuators are operated by means of only one control lever.
The control circuit for a construction machine according to the present invention has following constitution.
The present invention comprises: a control lever for carrying out operations of a first actuator and a second actuator in common; a switching valve or a selector valve for supplying pilot pressure output from a remote control valve by means of operation of the control lever to a control port in any one of the first and the second actuators; a control member for supplying a switching signal to the switching valve; a detector for detecting whether the pilot pressure is output from the remote control valve or not; and a switching controller for switching a change-over position in the switching valve from the first actuator to the second actuator when the switching signal is output from the control member and holding the position at the second actuator when output of the pilot pressure is detected by the detector.
According to the present invention, if the control member is operated, the switching valve switches a pilot pressure supply place to which the pilot pressure is output from the remote control valve of the control lever, from the first actuator to the second actuator, and then the detector detects the pilot pressure if the pilot pressure appears in a pilot line by means of operation of the control lever. The switching control means holds the switching valve at the second actuator when the switching signal is output from the control member and when output of the pilot pressure is detected by the detector. Thereby, switching from the first actuator to the second actuator does not occur as long as the control member is not operated. Also, when the control lever is operated in a state that the control member is operated to switch the position of switch to the second actuator, the position cannot be switched to the first actuator even if the control member is off, as long as the control lever is not restored in neutral position. Therefore, wrong operation can be prevented in switching. Also, even if a finger is taken off the control member during operation, a bad situation that the position of switch is switched to other actuator can be prevented.